A project to add "smart" functionality with an ESP-32 into a thirty year old (1993) but fully functioning (and reliable) alarm system.
https://github.com/blaniosh/alarm
I have converted a 1993 wired alarm to a smart system using an ESP32 module. I can set/unset it remotely using a key or via a dedicated webpage. The status (set, unset or alarm triggered) is presented by the webpage and an email.
Sorry to come to this thread late but one cost effective option I can recommend is to run a VPN server on a Raspberry Pi 4. I have been very impressed with PiVPN running Wireguard.